The broad, long-term objective of the proposed research is to improve understanding of the cell biology of heart attacks, particularly the events which occur during ischemia and upon reperfusion of reversibly injured myocardial tissue. The improvement in revascularization procedures in treatment of coronary atherosclerosis has paradoxically increased the risk of reperfusion injury leading to impaired myocardial performance and possibly fatal arrhythmias. Considerable evidence indicates oxygen centered free radical formation upon reperfusion of previously ischemic tissue is responsible for reperfusion injury. The research proposed will explore cellular locations of enzymatic activities and injuries related to free radical formation and quenching, attempt to determine the source and site of formation of free radicals, and determine the site of action of exogenous agents that minimize reperfusion injury. These aims will be accomplished by the following two studies: 1) definition of reperfusion injury in isolated working hearts subjected to regional ischemia, using physiological, biochemical, and ultrastructural parameters; 2) localization of lipid peroxides, xanthine oxidase (XO), and both endogenous and exogenous superoxide dismutase (SOD) and catalase (CAT) in normal and reperfused heart tissue. Heart preparations will be used comparatively. Identification and localization of enzyme activities will be accomplished by use of antibodies to different forms of SOD, CAT, and XO, and by diaminobenzidine-linked histochemical methods that can localize oxidase activities and lipid peroxides. This research will increase knowledge of cell biology and myocytes, and may provide a basis for more effective interventions to prevent pathologically and clinically induced reperfusion injury.